The invention relates to cable gels.
It is known to use thixotropic cable gels as filling material in optical fibre cables.
DE 36 22 211 describes a filling material which contains from 50 to 99 wt. % polypropylene glycol, especially having a molar mass from 2000 to 3500, and from 50 to 1 wt. % highly disperse silicon dioxide as thixotropic agent.
U.S. Pat. No. 4,701,016 describes a filling material which contains from 77 to 95 wt. % of an oil or of a mixture of oils and from 2 to 15 wt. % colloidal particles. They may additionally contain up to 15 wt. % of an elastomer. There are used as oils paraffin oil, naphthenic oil, polybutene oil, triglyceride-based vegetable oil, polypropylene oil, chlorinated paraffin oil and polyesters. The colloidal particles consist of hydrophobic fumed silica, precipitated silica and clay.
In U.S. Pat. No. 5,348,669 there is described a filling material which contains from 75 to 95 wt. % of a polypropylene glycol having a molar mass of at least 3000, and from 2 to 20 wt. % of either a hydrophilic or hydrophobic fumed silica. The filling material may additionally contain an antioxidant in order to improve temperature resistance, and an elastomer in order to reduce oil separation.
U.S. Pat. No. 5,433,872 describes a filling material which contains from 75 to 95 parts of a liquid to semi-solid polyol having a molar mass of at least 4000, small amounts of an unsaturated compound, and from 1 to 15 wt. % of a fumed silica as thickener. The filling material may additionally contain a thermoplastic elastomer in order to reduce oil separation.
DE 38 39 596 describes a thixotropic gel and its preparation based on a synthetic hydrocarbon oil and a hydrophobic thixotropic agent. The cable gel is suitable as filling material in the production of optical fibre cables.
It is also known from the series of documents Pigmente No. 63, Degussa AG, 1995, page 28 to 30, that compressing hydrophilic fumed silica enables the silica to be incorporated into the binder more rapidly, for example using a planetary mixer or a planetary dissolver. Incorporation is understood to be the time required until the finely divided silica has disappeared completely from the surface of the binder and is wetted with the binder. Depending on the size of the batch, the dispersing device and the recipe, the incorporation time can be up to several hours and is accordingly the step that determines the speed of production of the product in many applications. Furthermore, because of the increased density of the silica, reduced dust formation of the silica is achieved. The smaller volume of the compressed silica can also be of advantage when planning the system of dispersing devices.
It is a disadvantage that the viscosity of the silica-containing binder falls in most applications as the tamped density increases. Likewise, the dispersibility of the silica deteriorates. A phenomenon which manifests itself in the form of stippling, for example, in the case of a silicone sealing composition and higher surface roughness. Both effects are significant disadvantages. For that reason, compressed hydrophilic fumed silica can be used only in relatively limited fields of application.
Accordingly, the object is to produce cable gels in which those disadvantages do not occur.